Steel or brass (5)
I believe the answer is:
nerve
This clue is a double definition.
'steel' is the first definition.
(I know that steel can be written as nerve)
'brass' is the second definition.
(I know that brass can be written as nerve)
'or' is the link.
(Other definitions for nerve that I've seen before include "Courage - cheek" , "Fibre that carries instructions to the brain" , "Fearlessness" , "Temerity" , "Fibre to carry instructions between brain and body" .)